I've never ran it in any of my discus tanks just the out flow from the filter for water movement and that's it I've never had a problem once I would think your fine with out it but if it makes you feel better its not going to hurt them if you run one
In my opinion the main thing with discus is to keep all your water params at correct levels and stable, make sure they have a varied diet (meaty as well as a high quality pellet food and I always would add in some NLS flake food to there diet to), and pristine water (usually I did weekly 60% water changes on my discus tank) and you should have no problems
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